Shape selective hydrocarbon conversion over pre-selectivated, activated catalyst

ABSTRACT

A process for a shape selective hydrocarbon conversion such as toluene disproportionation involves contacting a reaction stream under conversion conditions with a catalytic molecular sieve which has been pre-selectivated and concurrently activated by contact with a substantially aqueous solution of an organosilicon compound. The invention also includes a method for concurrently preselectivating and activating a catalyst and the shape selectivated, activated catalyst which results from this method.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to copending U.S. patent applications Ser.Nos. 850,104 and 850,105 both filed Mar. 12, 1992 which are hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a process for shape selectivehydrocarbon conversions such as the regioselective production ofpara-substituted compounds, e.g. para-xylene. The invention is alsodirected to a modified catalyst and method of modifying the catalyst. Acatalytic molecular sieve is modified by treatment with an aqueoussolution of a water soluble organosilicon compound. The catalyticactivity and selectivity of the molecular sieve are both increased bythe modification treatment.

2. Description of the Prior Art

The term shape-selective catalysis describes unexpected catalyticselectivities in zeolites. The principles behind shape selectivecatalysis have been reviewed extensively, e.g. by N. Y. Chen, W. E.Garwood and F. G. Dwyer, "Shape Selective Catalysis in IndustrialApplications," 36, Marcel Dekker, Inc. (1989). Within a zeolite pore,hydrocarbon conversion reactions such as paraffin isomerization, olefinskeletal or double bond isomerization, oligomerization and aromaticdisproportionation, alkylation or transalkylation reactions are governedby constraints imposed by the channel size. Reactant selectivity occurswhen a fraction of the feedstock is too large to enter the zeolite poresto react; while product selectivity occurs when some of the productscannot leave the zeolite channels. Product distributions can also bealtered by transition state selectivity in which certain reactionscannot occur because the reaction transition state is too large to formwithin the zeolite pores or cages. Another type of selectivity resultsfrom configurational diffusion where the dimensions of the moleculeapproach that of the zeolite pore system. A small change in dimensionsof the molecule or the zeolite pore can result in large diffusionchanges leading to different product distributions. This type of shapeselective catalysis is demonstrated, for example, in toluene selectivedisproportionation to p-xylene.

The synthesis of para-xylene is typically performed by methylation oftoluene over a catalyst under conversion conditions. Examples are thereaction of toluene with methanol as described by Chen et al., J. Amer.Chem. Sec. 1979, 101, 6783, and toluene disproportionation, as describedby Pines in "The Chemistry of Catalytic Hydrocarbon Conversions",Academic Press, N.Y., 1981, p. 72. Such methods typically result in theproduction of a mixture including para-xylene, ortho-xylene, andmeta-xylene. Depending upon the para-selectivity of the catalyst and thereaction conditions, different percentages of para-xylene are obtained.The yield, i.e., the amount of feedstock actually converted to xylene,is also affected by the catalyst and the reaction conditions.

Previously known toluene methylation reactions typically provide manyby-products such as those indicated in the following formula:

Thermodynamic Equilibria for Toluene Conversion to the ProductsIndicated ##STR1##

One method for increasing para-selectivity of zeolite catalysts is tomodify the catalyst by treatment with "selectivating agents". Varioussilicon compounds have been used to modify catalysts to improveselectivity in hydrocarbon conversion processes. For example, U.S. Pat.Nos. 4,145,315, 4,127,616 and 4,090,981, describe the use of a siliconecompound dissolved in an organic solvent to treat a zeolite. U.S. Pat.Nos. 4,465,886 and 4,477,583 describe the use of an aqueous emulsion ofa silicone to treat a zeolite. U.S. Pat. Nos. 4,950,835 and 4,927,979describe the use of alkoxysilanes carried by gases or organic solventsto treat a zeolite. U.S. Pat. Nos. 4,100,215 and 3,698,157 describe theuse of silanes in hydrocarbons, e.g., pyridine or ethers, to treat azeolite.

Some catalyst modification procedures, for example, U.S. Pat. Nos.4,477,583 and 4,127,616 have been successful in obtainingpara-selectivity, i.e., para-xylene/all xylenes, of greater than about90% but with commercially unacceptable toluene conversions of only about10%, resulting in a yield of not greater than about 9%, i.e., 10%×90%.Such processes also produce significant quantities of ortho-xylene andmeta-xylene thereby necessitating expensive separation processes inorder to separate the para-xylene from the other isomers.

Typical separation procedures comprise costly fractional crystallizationand adsorptive separation of para-xylene from other xylene isomers whichare customarily recycled. Xylene isomerization units are then requiredfor additional conversion of the recycled xylene isomers into anequilibrium mixture comprising para-xylene.

Those skilled in the art appreciate that the expense of the separationprocess is proportional to the degree of separation required. Therefore,significant cost savings are achieved by increasing selectivity to thepara-isomer while maintaining commercially acceptable conversion levels.

The activity of a zeolite is an important consideration in acid-typecatalysis such as toluene disproportionation. Silicious zeolites may beconsidered to contain SiO₄ --tetrahedra. Substitution for thetetravalent element by a trivalent element such as aluminum produces anegative charge which must be balanced. If this is done by a proton, thematerial is acidic and active. The activity of zeolite catalysts hasbeen described in terms of its Alpha Value.

Various methods have been devised for enhancing the catalytic activity,i.e., the alpha of zeolite materials. U.S. Pat. No. 4,871,702 describesammonia activation of zeolites by contacting a zeolite and a solidsource of aluminum with an aqueous ammonium solution under ammonia gaspressure. U.S. Pat. No. 4,665,248 describes treating a mixture ofzeolite and a solid source of aluminum with liquid water in the presenceof alkali metal cation. U.S. Pat. No. 4,568,787 discloses contacting ahigh silica zeolite with aluminum chloride vapor and hydrolyzing. U.S.Pat. No. 4,576,805 describes enhancing catalytic activity of a zeoliteby contacting with a volatile metal halide compound to incorporate themetal into the crystalline lattice of the zeolite.

A method for simultaneous silicon modification for selectivity andactivity enhancement of a catalyst would have important application inshape-selective catalysis.

Accordingly, it would be highly advantageous to provide a shapeselective hydrocarbon conversion process such as toluenedisproportionation over a shape selective, highly active catalyst.

SUMMARY OF THE INVENTION

The invention is a process for shape selective hydrocarbon conversionssuch as the regioselective production of para-xylene. A reaction streamcontaining hydrocarbon feed such as toluene is contacted underhydrocarbon conversion conditions with a molecular sieve catalyst whichhas been concurrently pre-selectivated and activated by treating with acomposition which includes a substantially aqueous solution of a watersoluble organosilicon compound as a first silicon source. In toluenedisproportionation, the reaction stream may also contain a secondsilicon source. These reaction conditions in toluene disproportionationare suitable to provide a single pass para-xylene product, relative toall C₈ products, of at least about 90% and at least 15% tolueneconversion.

The invention is also a method for modifying a molecular sieve catalysthaving a Constraint Index of 1-12 by treating with a composition whichincludes a substantially aqueous solution of water soluble organosiliconcompound as a first silicon source, and then calcining. The catalyst maybe subsequently contacted with a mixture of a second silicon sourcewhich is a high-efficiency, para-xylene selectivating agent and tolueneat reaction conditions for converting toluene to xylene. The molecularsieve thus treated has greatly enhanced activity and selectivity. Theinvention also includes the modified catalyst.

Advantageously, a highly selective and highly active catalyst can beprovided in the modification method.

Furthermore, in the modification method, the use of aqueous solution ofsilicon sources is more cost efficient relative to organic solvent andaqueous emulsion procedures. The potentially hazardous distillation andcondensation of organic solvents is avoided. Furthermore, improveddeposition uniformity is provided using aqueous solutions compared toaqueous emulsions.

In addition, a shape selective hydrocarbon conversion process over themodified catalyst shows enhanced product selectivity with goodconversion.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is useful in shape selective hydrocarbonconversion processes such as in converting various aromatics,particularly toluene to commercially useful para-substituted benzenes,particularly para-xylene.

Molecular sieves to be used in the process of the invention includeintermediate pore zeolites. Such medium pore zeolites are considered tohave a Constraint Index from about 1 to about 12. The method by whichConstant Index is determined is described fully in U.S. Pat. No.4,016,218, incorporated herein by reference. Molecular sieves whichconform to the specified values of Constraint Index for intermediatepore zeolites include ZSM-5, ZSM-11, ZSM-5/ZSM-11 intermediate, ZSM-12,ZSM-21, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, ZSM-50, MCM-22 andZeolite Beta which are described, for example, in U.S. Pat. Nos.3,702,886 and Re. No. 29,949, 3,709,979, 3,832,449, 4,046,859,4,556,447, 4,076,842, 4,016,245, 4,229,424, 4,397,827, 4,954,325,3,308,069, Re. 28,341 and EP 127,399 to which reference is made fordetails of these molecular sieves. These zeolites may be produced withdiffering silica:alumina ratios ranging from 12:1 upwards. They havebeen, in fact, be produced from reaction mixtures from which aluminum isintentionally excluded, so as to produce materials having extremely highsilica:alumina ratios which, in theory at least may extend up toinfinity. Preferred intermediate pore zeolites include ZSM-5, ZSM-11,ZSM-12, ZSM-35 and MCM-22. Particularly preferred is ZSM-5.

In the invention, the catalyst preferably has a silica-alumina ratioless than 100 preferably about 20-80 and an alpha value greater than100, for example about 150-2000.

The Alpha Value is an approximate indication of the catalytic crackingactivity of the catalyst compared to a standard catalyst and it givesthe relative rate constant (rate of normal hexane conversion per volumeof catalyst per unit time.) It is based on the activity of the amorphoussilica-alumina cracking catalyst taken as an Alpha of 1 (RateConstant=0.016 sec⁻¹). The Alpha Test is described in U.S. Pat. No.3,354,078 and in The Journal of Catalysis, Vol. 4, pp. 522-529 (August1965): Vol. 6, p. 278 (1966); and Vol. 61, p. 395 (1980), eachincorporated herein by reference as to that description. It is notedthat intrinsic rate constants for many acid-catalyzed reactions areproportional to the Alpha Value for a particular crystalline silicatecatalyst (see "The Active Site of Acidic Aluminosilicate Catalysts, "Nature, Vol. 309, No. 5959, pp. 589-591, Jun. 14, 1984). Theexperimental conditions of the test used herein include a constanttemperature of 538° C. and a variable flow rate as described in detailin the Journal of Catalysis, Vol. 61, p. 395.

Since toluene disproportionation is an acid-type catalysis and requiresa catalyst having inherent acid activity, i.e., an elevated alpha, asilicon modification of the catalyst which increases alpha is highlyadvantageous. A silicon modification using an aqueous solution of anorganosilicon compound has been unexpectedly found to greatly increasealpha while concurrently yielding a catalyst with increasedpara-selectivity.

The catalyst is modified, i.e., concurrently pre-selectivated andactivated, by contact with an aqueous solution of an organosiliconcompound. By "pre-selectivation" is meant pretreatment of the catalystto lower non-shape selective surface acid activity and to increase therate of subsequent selectivation using para-xylene selectivating agents.

Organosilicon compounds useful herein are water soluble and may bedescribed as organopolysiloxanes. The preferred compounds arepolyalkylene oxide modified organopolysiloxanes. The organopolysiloxanesare preferably larger than the pores of the catalyst and do not enterthe pores.

The organopolysiloxanes include polysiloxanes having alkyl, alkoxy,aryl, aryloxy, arylalkyl or alkylaryl side groups. The amount ofalkylene oxide groups in the organopolysiloxanes can be increased toovercome any hydrophobicity. Alkyl includes 1 to 12 carbons. Arylincludes 6 to 10 carbons. Preferred organopolysiloxanes contained methyland/or ethyl groups.

Water soluble organosilicon compounds are commercially available as, forexample, SAG-5300, manufactured by Union Carbide, conventionally used asan anti-foam, and SF 1188 manufactured by General Electric.

The organosilicon compound is preferably dissolved in an aqueoussolution in an organosilicon compound/H₂ O weight ratio of from about1/100 to about 1/1.

A "solution" is intended to mean a uniformly dispersed mixture of one ormore substances at the molecular or ionic level. The skilled artisanwill recognize that solutions, both ideal and colloidal, differ fromemulsions.

The catalyst is contacted with a substantially aqueous solution of theorganosilicon compound at a catalyst/organosilicon compound weight ratioof from about 100 to about 1, at a temperature of about 10° C. to about150° C., at a pressure of about 0 psig to about 200 psig, for a time ofabout 0.1 hour to about 24 hours, the water is preferably removed, e.g.,by distillation, or evaporation with or without vacuum, and the catalystis calcined.

Shape Selective Conversions

Zeolites modified in accordance with the invention are generally usefulas catalysts in shape selective hydrocarbon conversion processesincluding cracking reactions involving dewaxing of hydrocarbonfeedstocks; isomerization of alkylaromatics; oligomerization of olefinsto form gasoline, distillate, lube oils or chemicals; alkylation ofaromatics; transalkylation of aromatics; conversion of oxygenates tohydrocarbons; rearrangement of oxygenates; and conversion of lightparaffins and olefins to aromatics.

Dewaxing

The subject catalysts have good cracking and hydrocracking activity andmay be used to convert paraffins from high to low molecular weightsubstances in dewaxing processes. The catalysts of the invention may beused in processes such as those described, for example, in U.S. Pat.Nos. 3,700,585, Re. 28,398, 3,968,024 and 4,181,598 which areincorporated herein by references. The term dewaxing means the removalof those hydrocarbons which will readily solidify (waxes) from petroleumstocks. Hydrocarbon feeds which can be treated include lubricating oilstocks as well as those which have a freeze point or pour point problem,i.e., petroleum stocks boiling above 350° F. The dewaxing can be carriedout at either cracking or hydrocracking conditions.

In U.S. Pat. No. 3,700,585 and Re. 28,398 to Chen et al., typicalcracking conditions include a liquid hourly space velocity (LHSV)between about 0.5 and 200, a temperature between about 288° C. (550° F.)and 590° C. (1100° F.), a pressure between about subatmospheric andseveral hundred atmospheres over ZSM-5 type catalysts. Typicalhydrocracking conditions include a liquid hourly space velocity betweenabout 0.1 and 10, a temperature between about 340° C. (650° F.) and 538°(1000° F.), a pressure between about 100 and 3000 psig, and a hydrogento hydrocarbon mole ratio between about one and 20. U.S. Pat. No.3,968,024 describes similar conversions using ZSM-5 of small crystalsize. U.S. Pat. No. 4,181,598 describes shape selective cracking toproduce lubes.

Isomerization of alkylaromatics

The modified catalysts of the invention are also advantageously used inthe isomerization of alkylaromatics in conversion reactions of the typedescribed, for example, in U.S. Pat. Nos. 3,856,872, 3,856,873, Re.30,157, 4,101,595, 4,101,597, 4,312,790, Re. 31,919 and 4,224,141 whichare herein incorporated by reference.

In U.S. Pat. No. 3,856,872 to Morrison, there is described a process forconverting C₈ aromatics xylene and ethylbenzene to para-xylene(octafining) at a temperature of 550° F. (288° C.) to 900° F. (482° C.),a pressure of 150 to 300 psig, and a liquid hour space velocity (LHSV)of 1 to 200 over an acid form catalyst containing metal such as platinumor nickel and hydrogen.

In U.S. Pat. No. 3,856,873 to Burress, mixtures of C₈ aromatichydrocarbons are isomerized to para-xylene by contact in vapor phasewith zeolite at a temperature of 500° F. (260° C.) to 1000° F. (538°C.), a pressure of 0 (atmospheric) to 1,000 psig, and a WHSV of 0.5 to250 with no added hydrogen. The catalyst is an acid ZSM-5, ZSM-12 orZSM-21.

U.S. Pat. No. 4,101,595 to Chen et al. describes the production ofpara-xylene from aromatics of 8 to 10 carbons over a dual functioncatalyst with a shape selective acid catalyzed step at a temperature of650° F. (343° C.) to 1000° F. (538° C.), a pressure of 50 to 500 psig, aLHSV of 0.1 to 100 and a molar of hydrogen/hydrocarbon of 0.1 to 15. Theacid form catalyst has a Constraint Index of 1 to 12, a silica/aluminaratio of at least 12, a crystal density of not less than 1.6 g/cc, maybe pre-coked, and includes Group VIII noble metal.

In U.S. Pat. No. 4,101,597 to Breckenridge, a C₈ feed is firstisomerized at 550° F. (288° C.) to 700° F. (371° C.) over a zeolitehaving a Constraint Index of 1 to 12, a silica/alumina ratio of at least12 and containing a metal having a hydrogenation/dehydrogenationfunction. A C⁹⁺ fraction produced during isomerization of C₈ isseparated from the other isomerization products, blended with hydrogenand toluene and contacted with a porous, acidic catalyst such as ZSM-5at 750° F. (399° C.) to 900° F. (482° C.). The catalyst has a ConstraintIndex of 1 to 12, a silica/alumina ratio of at least 12, and a metalproviding hydrogenation/dehydrogenation function.

In U.S. Pat. No. 4,224,141 to Morrison, C₈ aromatics are isomerized tobenzene, toluene and xylenes over a ZSM-5 which is reduced in activityby dilution with inert matrix, steaming or thermal treatment, very highsilica/alumina ratio, base exchange with alkali metal, coking or thelike. The conversion is at a temperature of 800° F. (427° C.) to 1000°F. (538° C.) in a low pressure isomerization unit at a pressure onlysufficient to overcome pressure drop through downstream processingequipment, e.g. below 100 psig, and a WHSV of 1 to 200.

In U.S. Pat. No. 4,312,790 and Re. 31,919 to Butter et al., a zeolite isincorporated with noble metal subsequent to zeolite crystallization butprior to catalyst extrusion. The catalyst is used for xyleneisomerization at a temperature of 500° F. (260° C.) to 1000° F. (540°C.), a pressure between 50 and 1000 psig, a WHSV of 1 to 50 and ahydrogen/hydrocarbon male ratio of 1 to 20.

Conversion of oxygenates to hydrocarbons

U.S. Pat. No. 4,476,330 to Kerr et al., herein incorporated byreference, describes the conversion of aliphatic oxygenates to a highermolecular weight compound by contacting with a zeolite having asilica/alumina ratio substantially greater than 10 at a temperature of70° F. (21° C.) to 1400° F. (760° C.). The feeds include lower aliphaticorganic oxygenates up to C₆, acetals, ketals, acid halides, alcohols,carboxylic acids, aldehydes, acid anhydrides, epoxides, ethers, esters,hemiacetals, gem diols, hydroxy acids, ketones, ketenes, lactones,peracids, peroxides, sugars, and especially alcohols, ethers and esters.Oligomerization of olefins

The modified catalysts of the invention are advantageously used in theoligomerization of olefins to form gasoline, distillate, lube oils orchemicals in conversion reactions of the type described, for example, inU.S. Pat. Nos. 4,517,399, 4,520,221, 4,547,609 and 4,547,613 which areherein incorporated by reference.

U.S. Pat. No. 4,517,399 to Chester et al. describes the conversion ofolefins of 3 to 18 carbons, e.g. propylene, to high viscosity, low pourpoint lubricating oils by contacting with ZSM-5 type zeolites havinglarge crystals of at least two microns. The conversion conditionsinclude a temperature of 350° F. (177° C.) to 650° F. (343° C.) apressure of 100 to 5000 psig, and a WHSV of 0.1 to 10.

U.S. Pat. No. 4,520,221 to Chen describes the polymerization of olefinsof 2 to 8 carbons, e.g. propylene, butylene, to high viscosity lubes,e.g. linear hydrocarbons, over highly siliceous, acidic ZSM-5 typecatalysts with surface acidity inactivated by treatment with base, e.g.bulky amines with a cross-section larger than about 5 Angstroms. Theconversion involves a one or two stage process with the polymerizationof lower olefins to linear materials, e.g. at about 200° C. over asurface poisoned zeolite, and oligomerization of the product over amodified or unmodified catalyst at a temperature of 50°-75° lower thanthe first stage, e.g. 150° C. Therefore, the temperatures range from 25°C. to 400° C., with a pressure of atmospheric to 1500 psi and a WHSV of0.04 to 1.0.

U.S. Pat. No. 4,547,609 to Dessau describes a two stage process wherebyin the first stage, light olefins of 2 to 6 carbons are oligomerized togasoline and distillate liquids including aliphatics of 10 to 20 carbonsover a zeolite having a crystal size greater than 0.5 micron atconditions including at a temperature of 500° F. (260° C.) or higher,e.g. a range of 500° F. (260° C.) to 800° F. (437° C.), a pressure ofatmospheric to 2000 psig and a WHSV of 0.1 to 20. In the second stage,the distillate fraction is converted to high viscosity lubes by contactwith a zeolite of smaller crystal size under milder conditions of atemperature about 200° F. (100° C.) to 500° F. (260° C.), a pressure ofatmospheric to 650 psig, and a WHSV less than one.

U.S. Pat. No. 4,547,613 to Garwood et al. describes converting olefinsof 2 to 16 carbons to high viscosity lube oil. A ZSM-5 type catalyst ispre-conditioned by contact with light olefins of 2 to 16 carbons, e.g.propylene at 400° .F (204° C.) to 1000° F. (538° C.), at a pressure of 0to 100 psig for 1 to 70 hours. Conversion conditions include atemperature of 350° F. (177° C.) to 650° F. (343° C.), a pressure of 400to 5000 psig and a WHSV of 0.1 to 10. The lube fraction may be subjectedto a hydrogenation step to stabilize.

Conversion of aromatics to dialkyl-substituted benzene

The modified zeolite catalysts of the invention are advantageously usedin the conversion of aromatics compounds to provide dialkyl-substitutedbenzene products which are highly enriched in the para-dialkylsubstituted benzene isomer. Conversion reactions of this type includearomatics alkylation, transalkylation and disproportionation. Aromaticsalkylations in which the catalysts of the invention can be used aredescribed, for example, in U.S. Pat. Nos. 3,755,483, 4,086,287,4,117,024 and 4,117,026 which are herein incorporated by reference.

As described in U.S. Pat. No. 3,755,483 to Burress, aromatichydrocarbons such as benzenes, naphthalenes, anthracenes and substitutedderivatives thereof, e.g. toluene and xylene, may be alkylated withalkylating agents such as olefins ethylene, propylene, dodecene, andformaldehyde, alkyl halides, and alkyl alcohols with 1 to 24 carbonsunder vapor phase conditions including a reactor inlet temperature up toabout 900° F. (482° C.), with a reactor bed temperature up to about1050° F. (566° ), at a pressure of about atmospheric to about 3000 psig,a ratio of aromatic/alkylating agent of about 1:1 to about 20:1 and aWHSV of 20 to 3000 over ZSM-12.

As described in U.S. Pat. No. 4,086,287 to Kaeding et al.,monoalkylbenzenes having alkyls of 1-2 carbons, such as toluene andethylbenzene, may be ethylated to produce a para-ethyl derivative, e.g.para-ethyltoluene at a temperature of from about 250° C. to about 600°C., a pressure of 0.1 atmospheres to 100 atmospheres, a weight hourlyspace velocity (WHSV) of 0.1 to 100, and a ratio of feed/ethylatingagent of 1 to 10 over a catalyst having an acid activity, i.e., alpha,of 2 to 5000, modified by precoking or combining with oxides ofphosphorus, boron or antimony to attain a catalyst with a xylenesorption capacity greater than 1 g/100 g of zeolite and an orthoxylenesorption time for 30% of said capacity of greater than 10 minutes, wheresorption capacity and sorption time are measured at 120° C. and a xylenepressure of 4.5±0.8 mm of mercury.

U.S. Pat. No. 4,117,024 to Kaeding describes a process for theethylation of toluene or ethylbenzene to produce p-ethyltoluene at atemperature of 350° C. to 550° C., a critical pressure of greater thanone atmosphere and less than 400 psig, with hydrogen/ethylene ratio of0.5 to 10 to reduce aging of the catalyst. The zeolite described in U.S.Pat. No. 4,117,024 has a crystal size greater then one micron, and ismodified as the catalyst in U.S. Pat. No. 4,086,287 to attain thesorption capacity described in U.S. Pat. No. 4,086,287.

U.S. Pat. No. 4,117,026 to Haag and Olson describes the production ofpara-dialkyl benzenes having alkyls of 1 to 4 carbons under conditionswhich vary according to the feed. When the feed includes monoalkylsubstituted benzenes having an alkyl of 1 to 4 carbons, olefins of 2 to15, or paraffins of 3 to 60 carbons or mixtures thereof, conversionconditions include a temperature of 250° C. to 750° , a pressure of 0.1to 100 atmospheres and a WHSV of 0.1 to 2000. For the disproportionationof toluene, the conditions include a temperature of 400° C. to 700° C.,a pressure of 1 to 100 atmospheres and a WHSV of 1-50. When the feedincludes olefins of 2 to 15 carbons including cyclic olefins, theconversion conditions include a temperature of 300° C. to 700° C., apressure of 1 to 100 atmospheres and a WHSV of 1 to 1000. When the feedincludes paraffins of 3 to 60 carbons, conditions include a temperatureof 300° C. to 700° C., a pressure of 1 to 100 atmospheres and a WHSV of0.1 to 100. However for lower paraffins of 3 to 5 carbons, thetemperature should be above 400° C. When the feed includes mixedaromatics such as ethylbenzene and toluene, and also optionally olefinsof 2 to 20 carbons or paraffins of 5 to 25 carbons, conversionconditions includes a temperature of 250° C. to 500° C. and a pressuregreater than 200 psig. In the absence of added aromatics, the olefinsand higher paraffins are more reactive and require lower severity ofoperation, e.g. a temperature of 250° C. to 600° C., preferably300°-550° C. The catalyst described in U.S. Pat. No. 4,117,026 ismodified as in U.S. Pat. No. 4,086,287.

Conversion of light paraffins and olefins to aromatics

The modified catalysts of the invention may also be used in theconversion of light paraffins and olefins to aromatics in processes ofthe type described, for example, in U.S. Pat. Nos. 3,760,024 and3,756,942 which are herein incorporated by reference.

U.S. Pat. No. 3,760,024 to Cattanach describes a process for theconversion of paraffins of 2 to 4 carbons and/or olefins to aromatics of6 to 10 carbons over a ZSM-5 type catalyst with or withouthydrogenation/dehydrogenation component. Conversion conditions include atemperature of 100° C. to 650° C., a pressure of 0 to 1,000 psig, a WHSVof 0.1 to 500 and a hydrogen/hydrocarbon ratio of 0 to 20.

U.S. Pat. No. 3,756,942 to Cattanach describes the conversion ofparaffins, olefins and naphthenes to aromatics over ZSM-5 typecatalysts. If the feed contains at least 35 wt. % olefins, conversion isat 650° F. (363° C.) to 1400° F. (760° C.). If the feed contains lessthan 35 wt. % olefins, the temperature is 900° F. (482° C.) to 1400° F(760° C.) with the absence of substantial added hydrogen. For both typesof feed, the pressure is atmospheric to 35 atmospheres and the WHSV 1 to15.

Pyridine synthesis

The modified catalysts of the invention are also advantageously used inthe synthesis of pyridine. Pyridine bases may be produced through thereactions of aldehydes and ketones with ammonia. The reaction ofacetaldehyde with ammonia in the presence of heterogenous catalysts atabout 350° C. to about 550° C. yields 2- and 4-methylpyridine.Acetaldehyde, formaldehyde and ammonia react to yield pyridine and3-methylpyridine. Pyridine synthesis is described, for example, in U.S.Pat. No. 4,675,410 to Feitler and U.S. Pat. No. 4,220,783 to Chang etal. which are herein incorporated by reference.

Caprolactam synthesis

Caprolactam is used in the commercial production of nylon. Caprolactammay be produced by Beckmann rearrangement of cyclohexane oxime over acidcatalysts including zeolites. The synthesis of caprolactam is described,for example, in U.S. Pat. No. 4,359,421 which is herein incorporated byreference.

Therefore, the modified catalysts of the present invention are suitablefor use in a variety of shape selective hydrocarbon conversion processesincluding as non-limiting examples, cracking hydrocarbons with reactionconditions including a temperature of from about 300° C. to about 700°C., a pressure of from about 0.1 atmosphere (bar) to about 30atmospheres and a weight hourly space velocity of from about 0.1 hr⁻¹ toabout 20 hr⁻¹ ; dehydrogenating hydrocarbon compounds with reactionconditions including a temperature of from about 300° C. to about 700°C., a pressure of from about 0.1 atmosphere to about 10 atmospheres andweight hourly space velocity of from about 0.1 to about 20; convertingparaffins to aromatics with reaction conditions including a temperatureof from about 300° C. to about 700° C., a pressure of from about 0.1atmosphere to about 60 atmospheres, a weight hourly space velocity offrom about 0.5 to about 400 and a hydrogen/hydrocarbon mole ratio offrom about 0 to about 20; converting olefins to aromatics, e.g. benzene,toluene and xylene, with reaction conditions including a temperature offrom about 100° C. to about 700° C., a pressure of from about 0.1atmosphere to about 60 atmospheres, a weight hourly space velocity offrom about 0.5 to about 400 and a hydrogen/hydrocarbon mole ratio offrom about 0 to about 20; converting alcohols, e.g. methanol, or ethers,e.g. dimethylether, or mixtures thereof to hydrocarbons includingolefins and/or aromatics with reaction conditions including atemperature of from about 275° C. to about 600° C., a pressure of fromabout 0.5 atmosphere to about 50 atmospheres and a liquid hourly spacevelocity of from about 0.5 to about 100; isomerizing xylene feedstockcomponents with reaction conditions including a temperature of fromabout 230° C. to about 510° C., a pressure of from about 3 atmospheresto about 35 atmospheres, a weight hourly space velocity of from about0.1 to about 200 and a hydrogen/hydrocarbon mole ratio of from about 0to about 100; disproportionating toluene with reaction conditionsincluding a temperature of from about 200° C. to about 760° C., apressure from about atmospheric to about 60 atmospheres and a weighthourly space velocity of from about 0.08 to about 20; alkylatingaromatic hydrocarbons, e.g. benzene and alkylbenzenes in the presence ofan alkylating agent, e.g. olefins, formaldehyde, alkyl halides andalcohols, with reaction conditions including a temperature of from about250° C. to about 500° C., a pressure of from about atmospheric to about200 atmospheres, a weight hourly space velocity of from about 2 to about2000 and an aromatic hydrocarbon/alkylating agent mole ratio of fromabout 1/1 to about 20/1; and transalkylkating aromatic hydrocarbons inthe presence of polyalkylaromatic hydrocarbons with reaction conditionsincluding a temperature of from about 340° C. to about 500° C., apressure of from about atmospheric to about 200 atmospheres, a weighthourly space velocity of from about 10 to about 1000 and an aromatichydrocarbon/polyalkylaromatic hydrocarbon mole ratio of from about 1/1to about 16/1.

In general, therefore, catalytic conversion conditions over a catalystcomprising the modified zeolite include a temperature of from about 100°C. to about 760° C., a pressure of from about 0.1 atmosphere (bar) toabout 200 atmospheres (bar), a weight hourly space velocity of fromabout 0.08 hr⁻¹ to about 2000 hr⁻¹ and a hydrogen/organic, e.g.hydrocarbon compound of from 0 to about 100.

Toluene Disproportionation

Toluene Disproportionation will be used as a representative shapeselective conversion. A catalyst treated in the manner described hereinyields a para-selective product in toluene disproportionation. Reactionconditions in the disproportionation include temperatures ranging fromabout 100° C. to about 600° C., preferably from about 300° C. to about500° C.; pressures ranging from about 0 to about 2000 psig, preferablyfrom about 15 to about 800 psig; a mole ratio of hydrogen tohydrocarbons from about 0 (i.e. no hydrogen is present) to about 10,preferably from about 1 to about 4; at a weight hourly space velocity(WHSV) from about 0.1 to about 100 hr⁻¹, preferably from about 0.1 toabout 10 hr⁻¹.

Normally a single pass conversion of a toluene stream results in aproduct stream which includes dimethylbenzenes having alkyl groups atall locations, i.e., ortho-, meta-, and para-xylenes. Furthermore, thexylenes are known to proceed in a reaction which produces unwantedethylbenzenes (EB) by the following reaction: ##STR2##

Previously, the purity of p-xylene with respect to all of the C₈products in a single pass has been limited to less than 90% whenisomerization is permitted. This efficiency is reduced somewhat by theproduction of ethylbenzene.

The present invention, however, provides high efficiency conversionwhich reduces production of ortho- and meta-isomers to the benefit ofthe desired para-isomer. The resulting product stream contains greaterthan a 90% purity of para-xylene. For example, the ortho-xylene isomercan be reduced to not more than about 0.5% of the total xylenes contentwhile the meta-xylene isomer can be reduced to less than about 5% of thetotal xylene content. Moreover, when the reaction system is properlytreated, such as by deposition of platinum on the molecular sieve, thepresence of ethylbenzene can be reduced to less than about 0.3% of theC₈ product.

As explained in greater detail herein, the present invention provides amethod for obtaining para-xylene at conversion rates of at least about15%, preferably at least about 20-25%, and with para-xylene purity ofgreater than 90%, preferably at least 95%, and most preferably about99%.

Therefore, higher para-xylene purity at commercially acceptableconversion rates than previously disclosed processes. The presentinvention thus allows for a significant reduction in process costspreviously associated with the separation of unwanted by-products.Processes of the prior art typically require expensive secondary andtertiary treatment procedures in order to obtain these efficiencies.

The present invention includes the regioselective conversion of tolueneto para-xylene by methylating toluene in a reaction stream containing atoluene feed with a trim selectivated catalytic molecular sieve whichhas been pre-selectivated and activated, with conversion reactionconditions to provide a single pass, para-xylene purity of at leastabout 90% based on the C₈ products. The trim selectivation methods aredescribed below. As used herein, the term "para-xylene purity" means thepercentage of para-xylene in all of the C₈ products which includeethylbenzene, para-xylene, ortho-xylene, and meta-xylene. Those skilledin the art will appreciate that the proximity of the boiling points ofthese C₈ products necessitates more expensive separation processeswhereas para-xylene may be more readily separated from other componentsin the product stream such as benzene, toluene, and para-ethyltoluene.

As used herein, the term "xylene-conversion product" indicates the totalamount of xylenes resulting from the disproportionation reaction. Theword "para-xylene" in this term is not intended to limit the scope ofthe present invention to the production of xylenes since otherpara-substituted aromatics may be produced.

In a preferred embodiment, the invention also includes a method for theregioselective production of para-xylene by passing a reaction streamwhich contains an aromatic feedstock, e.g., toluene, in a single pass,over a trim-selectivated catalytic molecular sieve, which ispre-selectivated, the single pass in the presence of hydrogen atreaction conditions suitable to provide para-xylene purity of greaterthan about 90%. The product stream may also include small amounts ofortho- and meta-xylene and trace amounts of impurities such asethylbenzene.

The toluene may be fed simultaneously with a high-efficiencyselectivating agent and hydrogen at reaction conditions until thedesired p-xylene selectivity, e.g., 90% or 95%, is attained, whereuponthe feed of selectivating agent is discontinued. This co-feeding ofselectivating agent with toluene will be termed "trim selectivation".Reaction conditions for this trim-selectivation step generally include atemperature of about 350°-540° C. and a pressure of aboutatmospheric--5000 psig. The feed is provided to the system at a rate ofabout 0.1-20 WHSV. The hydrogen is fed at a hydrogen to hydrocarbonmolar ratio of about 0.1-20.

The high efficiency para-xylene selectivating agent for trimselectivation preferably comprises a silicon containing compounddiscussed in greater detail below. For example, organic silicons such asphenylmethyl silicone, dimethyl silicone, and mixtures thereof aresuitable. According to one embodiment of the present invention, asilicone containing phenylmethylsilicon and dimethylsilicon groups in aratio of about 1:1 is co-fed to the system, while the other components,e.g., toluene and hydrogen, are fed in the amounts set forth above. Thehigh-efficiency para-xylene selectivating agent is fed in an amount ofabout 0.1%-50% of the toluene according to this preferred embodiment.Depending upon the percentage of selectivating agent used, the trimselectivation will preferably last for about 50-300 hours, mostpreferably less than 170 hrs.

The catalyst is pre-selectivated ex situ with a water solubleorganosilicon compound, then calcined and subsequently may be trimselectivated with a high efficiency para-xylene selectivating agent.After pre-selectivation, the catalytic molecular sieves for the presentinvention are preferably converted to the hydrogen form. The crystalsize of zeolites used herein is preferably greater than 0.1 micron.

As used herein, the term "high efficiency, p-xylene selectivating agent"as used for trim selectivation is used to indicate substances which willincrease the para-selectivity of a catalytic molecular sieve to thestated levels while maintaining commercially acceptable toluene toxylene conversion levels. Such substances include, for example, organicsilicon compounds such as phenylmethyl silicone, dimethylsilicone, andblends thereof which have been found to be suitable.

The trim selectivation of the catalyst is preferably performed with asilicone containing compound. An example of silicone compounds which canbe used in the present invention can be characterized by the generalformula: ##STR3## where R₁ is hydrogen, fluorine, hydroxy, alkyl,aralkyl, alkaryl or fluoro-alkyl. The hydrocarbon substituents generallycontain from 1 to 10 carbon atoms and preferably are methyl or ethylgroups. R₂ is selected from the same group as R₁, and n is an integer ofat least 2 and generally in the range of 3 to 1000. The molecular weightof the silicone compound employed is generally between about 80 andabout 20,000 and preferably within the approximate range of 150 to10,000. Representative silicone compounds include dimethylsilicone,diethylsilicone, phenylmethylsilicone, methylhydrogensilicone,ethylhydrogensilicone, phenylhydrogensilicone, methylethylsilicone,phenylethylsilicone, diphenylsilicone, methyltrifluoropropylsilicone,ethyltrifluoropropylsilicone, polydimethylsilicone,tetrachlorophenylmethyl silicone, tetrachlorophenylethyl silicone,tetrachlorophenylhydrogen silicone, tetrachlorophenylphenyl silicone,methylvinylsilicone and ethylvinylsilicone. The silicone compound neednot be linear but may be cyclic as for examplehexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane,hexaphenylcyclotrisiloxane and octaphenylcyclotetrasiloxane. Mixtures ofthese compounds may also be used as well as silicones with otherfunctional groups. Other silicon-containing compounds, such as silanesand siloxanes, may also be utilized.

Preferably, the kinetic diameter of the high efficiency, p-xyleneselectivating agent is larger than the zeolite pore diameter, in orderto avoid reducing the internal activity of the catalyst.

Before trim-selectivation, the catalyst is preselectivated, and asilicon compound is deposited on the external surface of the catalyst.

Following deposition of the silicon-containing compound inpre-selectivation, the catalyst is calcined. For example, the catalystmay be calcined in an oxygen-containing atmosphere, preferably air, at arate of 0.2° to 5° C./minute to a temperature greater 300° C. but belowa temperature at which the crystallinity of the zeolite is adverselyaffected. Generally, such temperature will be below 600° C. Preferablythe temperature of calcination is within the approximate range of 350°to 550° C. The product is maintained at the calcination temperatureusually for 1 to 24 hours.

While not wishing to be bound by theory, it is believed that theadvantages of the present invention are obtained, in part, by renderingacid sites on the external surfaces of the catalyst substantiallyinaccessible to reactants while increasing catalyst tortuosity. Acidsites existing on the external surface of the catalyst are believed toisomerize the para-xylene exiting the catalyst pores back to anequilibrium level with the other two isomers thereby reducing the amountof para-xylene in the xylenes to only about 24%. By reducing theavailability of these acid sites to the para-xylene exiting the pores ofthe catalyst, the relatively high level of para-xylene can bemaintained. It is believed that the high-efficiency, p-xyleneselectivity agents of the present invention block or otherwise renderthese external acid sites unavailable to the para-xylene by chemicallymodifying said sites.

In line with this theory, it is also believed that the presence ofhydrogen in the reaction zone during the trim selectivation is importantin order to maintain the desired high yields of para-xylene when asilicone compound is used as the high-efficiency para-xyleneselectivating agent. The importance of the hydrogen may be reduced inalternative embodiments by using a high efficiency para-xyleneselectivating agent comprising silane or some other compound whicheffectively renders the isomerizing acid sites on the external surfaceof the catalyst inaccessible.

The invention may utilize a high efficiency para-xylene selectivatingagent which includes a silicon compound wherein the silicon compound isintroduced by co-feeding, for example, at least one silicon compoundwith the toluene feedstock over a conversion catalyst at reactionconditions until the desired degree of selectivation is achieved, atwhich time the feed of selectivating agent may be discontinued.

The toluene feedstock preferably includes about 50% to 100% toluene,more preferably at least about 80% toluene in the toluene feedstock.Other compounds such as benzene, xylenes, and trimethylbenzene may alsobe present in the toluene feedstock without adversely affecting thepresent invention.

The toluene feedstock may also be dried, if desired, in a manner whichwill minimize moisture entering the reaction zone. Methods known in theart suitable for drying the toluene charge for the present process arenumerous. These methods include percolation through any suitabledesiccant, for example, silica gel, activated alumina, molecular sievesor other suitable substances, or the use of liquid charge dryers.

For the improved disproportionation process of this invention, thesuitable molecular sieve may be employed in combination with a supportor binder material such as, for example, a porous inorganic oxidesupport or a clay binder. While the preferred binder is silica, othernon-limiting examples of such binder materials include alumina,zirconia, magnesia, thoria, titanic, boria and combinations thereof,generally in the form of dried inorganic oxide gels or gelatinousprecipitates. Suitable clay materials include, by way of example,bentonite and kieselguhr. The relative proportion of suitablecrystalline molecular sieve to the total composition of catalyst andbinder or support may be about 30 to about 90 percent by weight and ispreferably about 50-80 percent by weight of the composition. Thecomposition may be in the form of an extrudate, beads or fluidizablemicrospheres.

Operating conditions employed in the improved process of the presentinvention may be adjusted to affect the para-selectivity and tolueneconversion rate. Such conditions include the temperature, pressure,space velocity, molar ratio of the reactants, and the hydrogen tohydrocarbon mole ratio. One preferred embodiment of the presentinvention includes contacting a catalytic molecular sieve with a toluenefeedstock which includes a silicone compound under conditions foreffecting vapor-phase disproportionation. Conditions effective foraccomplishing the high para-selectivity and acceptable toluenedisproportionation conversion rates include a reactor inlet temperatureof about 350°-540° C., preferably greater than about 400° C., a pressureof about atmospheric--5000 psig, preferably about 100 to 1000 psig, aWHSV of about 0.1-20, preferably about 2-4, and a hydrogen tohydrocarbon mole ratio of about 0.1-20, preferably about 2-4. Thisprocess may be conducted in either batch or fluid bed operation withattendant benefits of either operation readily obtainable.

The effluent is separated and distilled to remove the desired product,i.e., para-xylene, plus other by-products.

The catalyst may be further modified in order to reduce the amount ofundesirable by-products, particularly ethylbenzene. The state of the artis such that the reactor effluent from standard toluenedisproportionation typically contains about 0.5% ethylbenzeneby-product. Upon distillation of the reaction products, the level ofethylbenzene in the C₈ fraction often increases to about 3-4 percent.This level of ethylbenzene is unacceptable for polymer grade p-xylenesince ethylbenzene in the C₈ product, if not removed, degrades thequality of fibers ultimately produced from the p-xylene product.Consequently, ethylbenzene content must be kept low. The specificationfor ethylbenzene in the C₈ product has been determined by industry to beless than 0.3%. Ethylbenzene can be substantially removed byisomerization or by superfractionation processes. Removal of theethylbenzene by conventional isomerization would be impractical with thepresent invention since the xylene stream, which includes greater than90% para-xylene, would be concurrently isomerized to equilibrium xylenesreducing the amount of para-xylene in this xylene stream to about 24%.It is known in the art that the alternative procedure of removing theethylbenzene by superfractionation is extremely expensive.

In order to avoid the need for downstream ethylbenzene removal, thelevel of ethylbenzene by-product is advantageously reduced byincorporating a hydrogenation-dehydrogenation function in the catalyst,such as by addition of a metal compound such as platinum. While platinumis the preferred metal, other metals such as palladium, nickel, copper,cobalt, molybdenum, rhodium, ruthenium, silver, gold, mercury, osmium,iron, zinc, cadmium, and mixtures thereof may be utilized. The metal maybe added by cation exchange, in amounts of about 0.01-2%, typicallyabout 0.5%. The metal must be able to enter the pores of the catalyst inorder to survive a subsequent calcination step. For example, a platinummodified catalyst can be prepared by first adding the catalyst to asolution of ammonium nitrate in order to convert the catalyst to theammonium form. The catalyst is subsequently contacted with an aqueoussolution of tetraamine platinum(II) nitrate or tetraamine platinum(II)chloride. The metallic compound advantageously enters the pores of thecatalyst. The catalyst can then be filtered, washed with water andcalcined at temperatures of about 250° to 500° C. Thehydrogenation-dehydrogenation metal ions are preferably introduced intothe catalyst before pre-selectivation.

By the present process, toluene can be converted to aromaticconcentrates of high value, e.g., about 99% para-xylene based on all C₈products. In a typical embodiment of the present process, optimumtoluene conversion is found to be about 20-25 weight percent with apara-xylene purity of about 90-99%.

The following non-limiting examples illustrate the invention:

EXAMPLE 1

Silica-modified HZSM-5 was prepared by adding 2.5 g silica bound HZSM-5to 0.29 g organopolysiloxane, a dimethyl silicone fluid modified torender it water soluble (SAG-5300, Union Carbide). The water wasdistilled off and the residue was air calcined at 2° C. per minute to538° C., then six hours at 538° C. The silica-modified HZSM-5 productcontained 8.5% added silica.

The alpha value of the silica-modified catalyst was 1622 compared to 731for the parent zeolite.

COMPARATIVE EXAMPLES

Silica-modified HZSM-5 catalysts having similar silica loading andprepared by aqueous emulsion and organic solvent procedures decreasedthe alpha value of HZSM-5 from 180 to 52 and from 199 to 67respectively.

EXAMPLE 2

The catalyst prepared in Example 1 was tested for toluenedisproportionation at 400° C., 4.0 WHSV, 500 psig and a 2/1hydrogen/hydrocarbon ratio. Conversion was 28% indicating a very activecatalyst. Xylene equilibrium was 22% p-, 55% m- and 23% o-.

EXAMPLE 3

The catalyst prepared in Example 1 was trim selectivated using 1%phenylmethyl silicone in toluene feed at 446° C., 500 psig, 4.0 WHSV,and hydrogen/hydrocarbon ratio=2. The following table shows tolueneconversion and p-xylene selectivity as a function of time on stream. Thetrim selectivation substantially increased p-xylene selectivity from 24%to 90% at a commercially attractive 23% toluene conversion.

                  TABLE 1                                                         ______________________________________                                        Time on     Toluene       p-Xylene in                                         Stream, Hrs.                                                                              Conversion, 10+ %                                                                           Xylenes, Wt %                                       ______________________________________                                         2          51            24                                                   6          51            26                                                  24          40            47                                                  48          35            68                                                  72          32            78                                                  96          29            83                                                  165         23            90                                                  ______________________________________                                    

What is claimed is:
 1. A process for a shape selective hydrocarbonconversion comprises contacting a reaction stream comprising hydrocarbonto be converted, under conversion conditions, with a molecular sievecatalyst which has been preselectivated and activated by treating with asubstantially aqueous solution of a water-soluble organosiliconcompound.
 2. The process of claim 1 wherein the shape selectivehydrocarbon conversion is selected from a group consisting of dewaxingof paraffins, isomerization of alkylaromatics, oligomerization ofolefins, transalkylation of aromatics, alkylation of aromatics,conversion of oxygenates to hydrocarbons, rearrangement of oxygenatesconversion of paraffins to aromatics and conversion of olefins toaromatics.
 3. The process of claim 1 wherein the conversion conditionscomprise a temperature of from about 100° C. to about 760° C., apressure of about 0.1 atmosphere to about 200 atmospheres, a weighthourly space velocity of from about 0.08 hr⁻¹ to about 2000 hr⁻¹, and ahydrogen/hydrocarbon molar ratio of from about 0 to about
 100. 4. Theprocess of claim 1 wherein the shape selective hydrocarbon conversion istoluene disproportionation.
 5. The process of claim 1 wherein themolecular sieve comprises a zeolite having a Constraint Index from about1 to about
 12. 6. The process of claim 1 wherein the molecular sievecatalyst comprises ions selected from a group consisting of hydrogen,hydrogen precursor, metals of Periodic Table Group VIII and combinationsthereof.
 7. The process of claim 1 wherein the molecular sieve catalystcomprises molecular sieve crystals and matrix material.
 8. The processof claim 8 wherein the matrix material comprises silica.
 9. The processof claim 1 wherein the treating of the catalyst is with an organosiliconcompound in an organosilicon compound/H₂ O weight ratio of from about1/100 to about 1/1, at a molecular sieve/organosilicon compound weightratio of from about 100/1 to about 1/1, at a temperature of from about10° C. to about 150° C., at a pressure of from about 0 psig to about 200psig for a time of about 0.1 hours to about 24 hours.
 10. The process ofclaim 1 wherein the molecular sieve catalyst is calcined after beingtreated.
 11. The process of claim 1 wherein the organosilicon compoundcomprises a water soluble polysiloxane which is modified by polyalkyleneoxide.
 12. The process of claim 11 wherein the polyalkylene oxide ispolyethylene oxide modified.
 13. A process for disproportionation oftoluene to xylene comprising:contacting a reaction stream whichcomprises toluene, under reaction conditions for converting toluene top-xylene, with a molecular sieve catalyst wherein the molecular sievecatalyst has been preselectivated and activated by treating with asubstantially aqueous solution of a water-soluble organosiliconcompound.
 14. The process of claim 13 wherein the reaction conditionscomprise a temperature from about 100° C. to about 600° C., a pressurefrom about 0 to about 2000 psig, a weight hourly space velocity (WHSV)between about 0.1 hr⁻¹ and about 100 hr⁻¹, and a hydrogen/hydrocarbonmole ratio from 0 to about
 20. 15. The process of claim 13 wherein themolecular sieve comprises a zeolite having a Constraint Index from about1 to about
 12. 16. The process of claim 13 wherein the molecular sievecatalyst comprises ions selected from a group consisting of hydrogen,hydrogen precursor, metals of Periodic Table Group VIII and combinationsthereof.
 17. The process of claim 13 wherein the molecular sievecatalyst comprises molecular sieve crystals and matrix material.
 18. Theprocess of claim 17 wherein the matrix material comprises silica. 19.The process of claim 13 wherein the treating of the catalyst is with anorganosilicon compound in an organosilicon compound/H₂ O weight ratio offrom about 1/100 to about 1/1, at a molecular sieve/organosiliconcompound weight ratio of from about 100/1 to about 1/1, at a temperatureof from about 10° C. to about 150° C., at a pressure of from about 0psig to about 200 psig for a time of about 0.1 hours to about 24 hours.20. The process of claim 13 wherein the molecular sieve catalyst iscalcined after being treated.
 21. The process of claim 13 wherein theorganosilicon compound comprises a water soluble polysiloxane which ismodified by polyalkylene oxide.
 22. The process of claim 21 wherein thepolyalkylene oxide is polyethylene oxide.
 23. The process of claim 13wherein the reaction stream further comprises a secondsilicon-containing compound which is a high efficiency para-xyleneselectivating agent.
 24. The process of claim 23 wherein the secondsilicon-containing compound is fed with the reaction stream for at leastone hour.
 25. The process of claim 23 wherein the high efficiencypara-xylene selectivating agent comprises a silicone compound.
 26. Theprocess of claim 25 wherein the silicone compound comprises a mixture ofphenylmethylsilicone and dimethylsilicone.
 27. The process of claim 25wherein the reaction stream comprises at least 80% toluene and at least0.1% silicone compound.
 28. The process of claim 23 wherein thecontacting provides a single pass para-xylene product relative to all C₈products of at least about 90% with at least about 15% tolueneconversion.